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Controlling Emissive Properties by Intramolecular Hydrogen Bonds: Alkyl and Aryl meso ‐Substituted Porphycenes
Author(s) -
Listkowski Arkadiusz,
Masiera Natalia,
Kijak Michał,
Luboradzki Roman,
Leśniewska Barbara,
Waluk Jacek
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202005440
Subject(s) - intramolecular force , chemistry , aryl , alkyl , quantum yield , photochemistry , singlet state , porphyrin , delocalized electron , excited state , structural isomer , hydrogen bond , fluorescence , computational chemistry , molecule , stereochemistry , organic chemistry , quantum mechanics , nuclear physics , physics
Porphycene, a porphyrin isomer, is an efficient fluorophore. However, four‐fold meso substitution with alkyl groups decreases the fluorescence quantum yield by orders of magnitude. For aryl substituents, this effect is small. To explain this difference, we have synthesized and studied a mixed aryl‐alkyl‐substituted compound, 9,20‐diphenyl‐10,19‐dimethylporphycene, as well as the 9,20‐diphenyl and 9,20‐dimethyl derivatives. Analysis of the structural, spectroscopic, and photophysical data of the six porphycenes, combined with quantum chemical calculations, shows a clear correlation between the strength of the intramolecular NH⋅⋅⋅N hydrogen bonds and the efficiency of the radiationless depopulation of the lowest‐excited singlet state. This result led us to propose a model in which the delocalization of the inner protons in the cavity of the macrocycle is responsible for the nonradiative deactivation channel. The applicability of the model is confirmed by the literature data for other alkyl‐ or aryl‐substituted porphycenes. The finding of a correlation between structural and emissive characteristics enables a rational design of porphycenes with desired photophysical properties.